Targeted chemical analysis of dilute samples can be expensive difficult with current methods and systems. For example, if small amounts of an analyte are present in a sample, it is desirable to remove the analyte from the sample or concentrate the analyte in order to detect its presence. These constraints can make it difficult in situations were large volume samples must be shipped and processed in order to be used.
Similar issues exist when a sample has a small volume. Sample must be conserved in order to be able to run tests in duplicate. Simply diluting small volume samples to obtain a greater volume for testing is not feasible where the analyte of interest exists in low concentrations.
Solid phase extraction is a widely employed method for isolating chemical and biological substances of interest out of mixtures by adsorption or absorption. Solid phase extraction in modern chemical analysis is most commonly conducted in a column mode where the sample is flowed through an immobilized zone of porous adsorbent material by gravity, pumping or vacuum. However, accessory equipment is required to use the columns, columns clog when insolubles are present in the samples, columns are expensive (especially large columns to extract larger samples), and columns can vary in their performance because of variation in how well they are packed.
It is difficult to avoid using columns when using chromatographic extraction particles because without the protection of the column apparatus, many chromatographic extraction particles readily fragment by abrasion to small particulates (fines) when a bag of them is handled or tumbled. This would contaminate the scientist and sample with fines that migrate out of the bag. Reproducibility is compromised and sample is lost.
Analysts often desire the ability to extract multiple analytes simultaneously by solid phase extraction. However, no single adsorbent column gives a good recovery for all of the analytes. While multiple columns may be used, this is expensive, as well as time and space consuming. It also not feasible to prepare a single column with multiple adsorbents since column preparation requires special hardware and many adsorbants particles are of different sizes which can lead to impeding the flow of sample through a column.
Solid phase microextraction (SPME) techniques can be used to extract small sample volumes. In SPME, the outside of a solid fused silica fiber, or the inside of a fused silica capillary tubing, is coated, covalently or noncovalently, with an organic polymer. However, the fibers are expensive, difficult to make, and fragile. Thinner fiber coatings reduce sensitivity and thicker coatings reduce analysis speed. Relatively few coatings are available since ease of fabrication is coating-dependent.
Expanded bed liquid chromatography is a technique for preparative isolation of analytes in large, usually industrial-level, liquid samples having interfering insolubles. The upward flow of the sample through a loose bed of the chromatographic particles achieves solid phase extraction. Unfortunately, it is difficult to set up and maintain conditions which achieve efficient extraction of analytes in a relatively short time, while also removing all of the undesired insolubles. If the flow rate is too fast, the extraction efficiency is lower and the chromatographic reagent particles are lost with the sample insolubles by the upwards solvent flow. If the flow rate is slow, sample insolubles are not removed enough, and the process becomes too slow to be cost effective.
Thus, there is a need for systems and methods of solid phase extraction that can be used to extract single or multiple analytes in a relatively short time from samples of a wide variety of matrices and of dilute and/or small volume.